Convert those old wads to HL2
Where is it and how do I make one?
This tutorial is a small introduction to skins.
Creating a Fading Spray
Using GIMP to make self illuminating textures
This covers creation of custom textures in the Source engine
Tutorial on making a spray decal that contains a full range of transparency, such as text or graffiti like used in HL2.
In this tutorial you will learn how to create and implent normal maps into your custom source engine textures. Normal maps are textures that make your original texture look 3d.
how to make an animated texture work for you in Half-Life. You will need these programs: Photoshop and VTFEdit
Pixelated Sprite Sprays
Visible representation of water textures
This tutorial will show you how to create custom textures for use in creating maps for the Source engine
Custom particles in maps & spritesheet VTFs
This tutorial will cover the basics of reskinning a model for Hammer and HalfLife2.
Surface Materials for Source
How to painlessly make functional blend textures.
how to make those User Bars often seen on Forums.
This shows you how to make a blend texture for use on displacements and was created by Stadric.
How to make a transparent texture.
Creating Animated Sprays
Learn how to use custom textures in HL2 and CS:S.
How to create an alpha blending texture.
Merge HL2 textures to create new ones.
Our first tutorial is creating a static spray with no transparency.
How to create textures with Paint .NET and notepad.
Our second tutorial is creating a static spray with transparency.
how to make a signature for a forum, using pixel stretch technique to give a blurred matching background.
Creating your own decals
Guide for texture artists - creating material textures for source
What are source spraylogos? Spraylogos are images you can place on most surfaces in source multiplayer games with the exception of models.
This is the first of a series of texturing tutorials from Gronblad, and covers making a texture, and converting it for use in Hammer and HalfLife 2
how to extract a texture from the game, and then edit it.
This tutorial walks you through creating a material with transparency and then placing it into VGUI menu.
a pretty simple tutorial on making transparent textures
Some hints for you to manage bumpmapping with your custom textures
From bump mapping to phong shading - This tutorial covers a large number of texture effects. Look inside to discover how to give your textures an extra special touch.
This tutorial fom Stadric shows how to make textures look more realistic with depth and texture, by specular bumpmapping.
If I can find a photograph of something similar, it's fairly straightforward to turn it into a texture file.